System and method for adjusting printing operations in a direct-to-object printer having limited drop size variation printheads

ABSTRACT

A direct-to-object printer is configured to adjust a pixel density of a portion of contone image data for an image to be printed on a surface of a tapered object. The controller of the printer also filters the contone image data with a stochastic halftone filer to produce binary image data for the image to be printed on the tapered object. The adjustment in the pixel density for the portion of the image to be printed on the portion of the object having a circumference that is different than another portion of the surface at the uppermost portion of the image produces a more uniform appearance in the resulting printed image.

TECHNICAL FIELD

This disclosure relates generally to a system for printing onthree-dimensional (3D) objects, and more particularly, to systems thatprint on objects having tapered sides and sides of differentcircumferences.

BACKGROUND

Commercial article printing typically occurs during the production ofthe article. For example, ball skins are printed with patterns or logosprior to the ball being completed and inflated. Consequently, anon-production establishment, such as a distribution site or retailstore, for example, in a region in which potential product customerssupport multiple professional or collegiate teams, needs to keep aninventory of products bearing the logos of various teams followed in thearea. Ordering the correct number of products for each different logo tomaintain the inventory can be problematic.

One way to address these issues in non-production outlets is to keepunprinted versions of the products, and print the patterns or logos onthem at the distribution site or retail store. Printers known asdirect-to-object (DTO) printers have been developed for printingindividual objects. Operating these printers with known printingtechniques, such as two-dimensional (2D) media printing technology, toapply image content onto three-dimensional objects produces mixedresults. As long as the surface of the objects are relatively flat, theimages are acceptable. However, many products, such as cups, tumblers,and the like, have tapered surfaces, which adversely impact the printedimage quality. As used in this document, the word “tapered” means asurface that varies in circumference in a cross-process direction forthe printing of the object. To print these types of objects, theprinthead is positioned so it is parallel to the surface of the objectbeing printed as shown in FIG. 3. Alternatively, a tapered object can betilted so the face of the printhead(s) are parallel to the taperedobject surface. As the object is rotated about its longitudinal axis,the printhead is operated at a predetermined frequency to print lines ofink drops on the object. The separation of the printed ink drops along aprojection of the longitudinal axis of the object on the exterior of theobject is determined by the predetermined distance separating theinkjets in the printhead in that direction. As used in this document,the term “process direction” means a direction of rotation past theprinthead and the term “cross-process direction” means a direction alongthe surface of the object that joins the longitudinal axis at theopposite ends of the object. In this example, the frequency of inkjetfiring determines the resolution of the image in the process directionand the distance between the inkjets in the cross-process directiondetermines the most coarse resolution in the cross-process direction. Insome printing systems, the printhead is moved in the cross-processdirection by a predetermined distance to increase the resolution of theimage in the cross-process direction. For example, the inkjets in theprinthead of FIG. 3 are operated at a frequency that produces a processdirection resolution of 750 dpi and a resolution in the cross-processdirection of 75 dpi. By moving the printhead in the cross-processdirection by 1/600^(th) of one inch following each complete revolutionof the first seven revolutions in an eight revolution printing process,the resolution is increased to 600 dpi in the cross-process directionsince eight groups of 75 dpi lines are printed within an inch withoutoverlap. Thus, the final resolution in this example produces an imagewith a resolution of 750 dpi in the process direction and 600 dpi in theprocess direction.

With known 2D printing processes, the density of the ink image, whichcan be measured in drops per inch (dpi) or mass per unit area, on theportions of the product having the larger circumference variessignificantly from those having a lesser circumference. This problemarises because a greater area of the object rotates past the printheadwhile the smaller circumference also rotates past the printhead. Thus,the portion having the larger circumference is moving at a greaterangular velocity than the smaller circumference portion. Consequently,the same amount of ink is distributed over a greater area at the largercircumference portion than the smaller circumference portion. Thisdistribution differential produces a less dense image at the largercircumference portion than the density of the image at the smallercircumference portion. If the desired image is supposed to be uniform indensity, then the printed image differs from the desired image. Anexample of this phenomenon is depicted in FIG. 4A, which is a 2D uniformimage to be printed on a tapered object, and FIG. 4B, which shows theresulting image printed on the object.

One method of addressing this issue is presented in U.S. Pat. No.9,333,741. The system in that document uses a printhead having two rowsof inkjets extending in the cross-process direction with each row having500 inkjets. The two rows are offset from one another in thecross-process direction and separated from each other in the processdirection by a constant distance. By timing the firing of the inkjets inone row so it ejects ink drops between the drops ejected by the otherrow, a single line in the cross-process direction having a pixel densityof 360 dpi can be obtained. When the circumference changes in thecross-process direction, the timing for the firing of the inkjets in thesecond line has to be adjusted to produce the single line. This timingparameter is calculated using the printing frequency and the differencebetween the circumference of the object opposite the inkjet and thecircumference of the object at the uppermost end of the image region.Then, the system reduces the pixel density within a single line by apercentage density and compares the reduced pixel density to eightvolumes for the ink drops that can be ejected by the inkjet to select anappropriate ink drop volume. Thus, the problem of printing on taperedobjects is solved by adjusting the timing of the firing of the inkjetsin the second row of inkjets and by increasing the drop volumes in thearea where less pixel density occurs or by decreasing the drop volumeswere high pixel density occurs. The printhead used in this systemincorporates this wide range of ink drop volume control because theprinthead has a relative low resolution in the cross-process directionand this system is configured to print an image on the object in asingle revolution of the object. Consequently, this system uses ink dropvolume variation to adjust pixel density in different areas of the imageon the object in an effort to make regions printed with different dropsizes appear to be uniform to the human eye when in fact it does nottruly have a uniform image density over the entire printed region.

Unfortunately, the solution presented in this system cannot be used inthe DTO printer discussed previously that prints images with aresolution of 750 dpi (process direction) by 600 dpi (cross-processdirection). This DTO system prints high resolution images withoutvarying the ink drop volumes. Since the inkjets in this type of DTOprinter cannot alter pixel density for an inkjet using a wide range ofink drop volumes, the approach of U.S. Pat. No. 9,333,741 is not usefulfor this type of system. Therefore, a printing process control systemthat produces quality images for products having varying circumferencediameters using printheads having little or no ink drop volumeregulation would be beneficial.

SUMMARY

A new direct-to-object (DTO) printing system using printheads havinglittle or no ink drop volume regulation is configured to produce inkimages having a uniform density on tapered or other circumferencevarying objects. The printing system includes at least one printhead,the printhead being configured to eject marking material, a supporthaving a first end and a second end, the at least one printhead beingpositioned opposite the support and between the first end and the secondend of the support, a holder configured to hold an object and to movealong the support between the first end and the second end of themember, an actuator operatively connected to the holder, the actuatorbeing configured to move the holder and an object within the holderalong the support to a position opposite the at least one printhead andto rotate the object, and a controller operatively connected to the atleast one printhead and the actuator. The controller is configured tooperate the actuator to move the holder and the object with the holderto the position opposite the at least one printhead, to operate theactuator to position a face of the at least one printhead parallel to asurface of an object to be printed that has a varying circumference andto rotate the object, to modify contone image data to adjust a pixeldensity of an image to be printed on the surface of the object, toproduce binary image data using the modified contone image data and astochastic halftone filter, and to operate inkjets within the at leastone printhead using the binary image data to form an image on the objectwith the varying circumference as the object rotates.

A method of operating a DTO printer using printheads having little or noink drop volume regulation produces ink images having a uniform densityon tapered or other circumference varying objects. The method includesoperating with a controller an actuator operatively connected to aholder to move the holder and an object having a varying circumferencewithin the holder to a position opposite at least one printhead in theprinting system, operating with the controller the actuator to positiona face of the at least one printhead parallel to a surface of an objectand to rotate the object, modifying with the controller contone imagedata of an image to be printed on a surface of the object to adjust apixel density of the image to be printed on the surface of the object,filtering with the controller the modified contone image data using astochastic halftone filter to produce binary image data, and operatinginkjets within the at least one printhead using the binary image data toform an image on the object with the varying circumference as the objectrotates.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of a printing system thatprints uniform density ink images on tapered surfaces of 3D objects areexplained in the following description, taken in connection with theaccompanying drawings.

FIG. 1 is a schematic diagram of a side view of a printing systemconfigured to process contone data of an image to be printed so theresulting processed data adjusts the operation of the printheads in theprinter for printing images on objects with varying circumferences.

FIG. 2A and FIG. 2B are a flow diagram of a process for printing objectsin the system of FIG. 1.

FIG. 3 depicts the positioning of a prior art printhead for forming anink image on a tapered object.

FIG. 4A depicts a uniform density image to be printed on a taperedobject in the prior art.

FIG. 4B depicts the actual prior art image printed on the tapered objectusing the unadjusted pixel data corresponding to the image shown in FIG.4A.

DETAILED DESCRIPTION

For a general understanding of the present embodiments, reference ismade to the drawings. In the drawings, like reference numerals have beenused throughout to designate like elements.

A printer 100 shown in FIG. 1 has been configured to process contoneimage data of an image to be printed on an object having a varyingcircumference to adjust the operation of the one or more printheads so amore uniform density image is produced. Printer 100 includes printheads118 in an array 112, a UV lamp 120, a member 116, and a holder 108 forobjects 104. While an array of printheads is depicted in FIG. 1, onlyone printhead is provided in some embodiments. In embodiments havingmultiple printheads, each printhead can eject a single color of ink,while in embodiments having only one printhead, the printhead can beconfigured to eject multiple colors of ink. Either the printheads or theholder 108 or both are configured to orient the surface of an object 104mounted to a holder 108 parallel to the faces of the printheads 118 asthe holder 108 holds the object in front of the array 112 of one or moreprintheads 118. The controller operates an actuator 128 to move theholder 118 along the support 116, which can be a pole, a beam, a rod, orthe like, so the object 104 in the holder 108 can be printed and thentreated before being ejected from the printer 100. For example, if oneor more of the printheads 118 in the array 112 ejects ultraviolet (UV)ink, the UV lamp 120 is operated by controller 124 to cure the UV ink.Controller 124 is configured to operate the one or more printheads inthe array 112 to eject marking material onto the surface of the object104. Latches 132 attach the holder 108 to the member 116. The controller124 is operatively connected to an actuator 122 to move the one or moreprintheads in the cross-process direction so multiple printing passescan be performed to increase the resolution of the image in thecross-process direction as described above.

A process for operating the printer 100 is shown in FIG. 2A and FIG. 2B.In the description of the process, statements that the process isperforming some task or function refers to a controller or generalpurpose processor executing programmed instructions stored innon-transitory computer readable storage media operatively connected tothe controller or processor to manipulate data or to operate one or morecomponents in the printer to perform the task or function. Thecontroller 124 noted above can be such a controller or processor.Alternatively, the controller can be implemented with more than oneprocessor and associated circuitry and components, each of which isconfigured to form one or more tasks or functions described herein.Additionally, the steps of the method may be performed in any feasiblechronological order, regardless of the order shown in the figures or theorder in which the processing is described.

The process 200 begins with an object 104 being secured within theholder 108 (block 204). The controller receives data through a userinterface that a tapered object is being printed (block 208). Thecontroller then adjusts the pixel density for each line of an image tobe formed on the object as the object rotates in front of the printheadarray 112 (block 212). The image data is contone data in which eachpixel value is a multi-bit value in a range, typically, of 0 to 255 forall of the colors the printhead is capable of printing, which arenormally cyan, magenta, yellow, and black, although other or additionalcolors can be used in the system. The controller is configured to adjustthe contone value of each pixel value by changing the original contonevalue in proportion to a ratio of the circumference of the object at thepixel's position on the object and the circumference of the object atthe top of the image. In other words:

Cyan(currentPixel)=Cyan(currentPixel)*Circumference(topPixel)/Circumference(currentPixel);

Magenta(currentPixel)=Magenta(currentPixel)*Circumference(topPixel)/Circumferenee(currentPixel);

Yellow(currentPixel)=Yellow(currentPixel)*Circumference(topPixel/Circumference(currentPixel);and

Black(currentPixel)=Black(currentPixel)*Circumference(topPixel)/Circumference(currentPixel).

As used in this document, the term “pixel density adjustment” meanschanging a contone data value for a pixel in an image using the ratio ofthe circumferences at the top of the image and at the current pixel'sposition. After the contone image data is modified, the contone data isfiltered using a stochastic halftone filter to produce binary pixel data(block 216). As used in this document, the term “stochastic halftonefilter” means an array of randomly distributed threshold values that areapplied to contone data that has been modified by the pixel densityadjustment percentage. Comparison of a contone data value to acorresponding threshold in the stochastic halftone filter results in abinary “1” or “0.” That is, a binary value of one corresponds to thefiring of the inkjet to eject an ink drop and a binary value of zerocorresponds to an inkjet not being activated. Consequently, pixeldensity in the resulting image is the result of fewer or more ink dropsbeing ejected rather than the volumes of the ink drops being adjusted.In contrast to the approach of using different drop sizes to printdifferent regions of an image on a tapered object, the pixel densityadjustment and stochastic halftone filtering of the adjusted pixel datayields a continuous modification of the image along the cross-processdirection of the changing circumference in the object.

Continuing with the process shown in FIG. 2A and FIG. 2B, once thebinary pixel data is produced, the controller operates the actuator 128that is operatively connected to the holder 108 to move the object andthe holder opposite the one or more printheads in the array 112 andpositions the object and printhead array so the surface of the objectand the face(s) of the one or more printheads 118 in the array 112 areparallel to one another (block 220). The controller 124 then operatesthe inkjets in the printheads using the binary pixel data to form atleast a portion on the image on the object as the controller operates anactuator to rotate the object (block 224). If the image is to be higherresolution (block 228), then the controller 124 is configured to operateactuator 122 to move the one or more printheads in the cross-processdirection so the one or more printheads eject ink drops betweenpreviously ejected ink drops in a previous pass to increase theresolution of the printed image (block 232). After all of the passes forprinting the image are preformed (block 236), the controller 124 thendetermines whether the ink in the image requires UV curing (block 240).If it does, the controller operates the actuator 128 to position theobject opposite the UV curing device 120 and then operates the device tocure the image (block 244). Otherwise, it operates the actuator 128 toreturn the object to the loading position for retrieval of the object(block 248). If the object was cured, the controller operates theactuator to return to the loading position after the curing is complete(block 248).

The approach of pixel density adjustment is useful not only forcontinuously tapered objects in a single direction, such as conical cupsand the like, but also for objects having other contoured shapes such ashourglass shaped objects or other objects having irregularly varyingcircumferences in the cross-process direction. Since the circumferenceat each pixel position in the image is compared to the circumference atthe top of the image for the pixel density adjustment disclosed herein,the pixel density adjustment is appropriate no matter the direction ofthe circumference variation.

It will be appreciated that variations of the above-disclosed apparatusand other features, and functions, or alternatives thereof, may bedesirably combined into many other different systems or applications.Various presently unforeseen or unanticipated alternatives,modifications, variations, or improvements therein may be subsequentlymade by those skilled in the art, which are also intended to beencompassed by the following claims.

1. A printing system comprising: at least one printhead, the printheadbeing configured to eject marking material; a support having a first endand a second end, the at least one printhead being positioned oppositethe support and between the first end and the second end of the support;a holder configured to hold an object and to move along the supportbetween the first end and the second end of the member; an actuatoroperatively connected to the holder, the actuator being configured tomove the holder and an object within the holder along the support to aposition opposite the at least one printhead and to rotate the object;and a controller operatively connected to the at least one printhead andthe actuator, the controller being configured to operate the actuator tomove the holder and the object with the holder to the position oppositethe at least one printhead, to operate the actuator to position a faceof the at least one printhead parallel to a surface of an object to beprinted that has a varying circumference and to rotate the object, tomodify contone image data to adjust a pixel density of an image to beprinted on the surface of the object, to produce binary image data usingthe modified contone image data and a stochastic halftone filter, and tooperate inkjets within the at least one printhead using the binary imagedata to form an image on the object with the varying circumference asthe object rotates.
 2. The printing system of claim 1, the controllerbeing further configured to adjust a pixel density of a line of contoneimage values in the contone image data for an inkjet in the at least oneprinthead, the line of contone image data corresponding to a firstportion of the surface of the object having a circumference that isgreater than or less than a second portion of the surface of the object.3. The printing system of claim 2 wherein the second portion of thesurface of the object is located at a position where an uppermost lineof the image is formed on the object.
 4. The printing system of claim 3,the controller being further configured to: adjust each contone imagevalue for the inkjet by multiplying each contone image value by a ratioof the circumference at the second portion to the circumference at thefirst portion.
 5. The printing system of claim 4 wherein the at leastone printhead ejects more than one color of ink.
 6. The printing systemof claim 5, the controller being further configured to: operate anotheractuator to move the at least one printhead by a predetermined distancein a cross-process direction; and operate the inkjets within the atleast one printhead after movement of the printhead by the predetermineddistance to increase a resolution of the image formed on the object inthe cross-process direction.
 7. The printing system of claim 6, thecontroller being further configured to: repeat the operation of theother actuator to move the at least one printhead by the predetermineddistance and the operation of the inkjets for a predetermined number oftimes.
 8. The printing system of claim 7 further comprising: a userinterface; and the controller is further configured to receive data fromthe user interface that identifies the object within the holder.
 9. Theprinting system of claim 8 wherein the at least one printhead isconfigured to eject ink drops with no more than two ink drop volumes.10. The printing system of claim 9 further comprising: an ultraviolet(UV) lamp configured to emit light in an UV range to cure UV curablemarking material ejected from the at least one printhead.
 11. A methodof operating a printing system comprising: operating with a controlleran actuator operatively connected to a holder to move the holder and anobject having a varying circumference within the holder to a positionopposite at least one printhead in the printing system; operating withthe controller the actuator to position a face of the at least oneprinthead parallel to a surface of an object and to rotate the object;modifying with the controller contone image data of an image to beprinted on a surface of the object to adjust a pixel density of theimage to be printed on the surface of the object; filtering with thecontroller the modified contone image data using a stochastic halftonefilter to produce binary image data; and operating inkjets within the atleast one printhead using the binary image data to form an image on theobject with the varying circumference as the object rotates.
 12. Themethod of claim 11 further comprising: adjusting with the controller apixel density of a line of contone image values in the contone imagedata for an inkjet in the at least one printhead, the line of contoneimage data corresponding to a first portion of the surface of the objecthaving a circumference that is greater than or less than a secondportion of the surface of the object.
 13. The method of claim 12 whereinthe second portion of the surface of the object is located at a positionwhere an uppermost line of the image is formed on the object.
 14. Themethod of claim 13 further comprising: adjusting with the controllereach contone image value for the inkjet by multiplying each contoneimage value by a ratio of the circumference at the second portion to thecircumference at the first portion.
 15. The method of claim 14 furthercomprising: operating with the controller the at least one printhead toeject more than one color of ink.
 16. The method of claim 15 furthercomprising: operating with the controller another actuator to move theat least one printhead by a predetermined distance in a cross-processdirection; and operating with the controller the inkjets within the atleast one printhead after movement of the printhead by the predetermineddistance to increase a resolution of the image formed on the object inthe cross-process direction.
 17. The method of claim 16 furthercomprising: repeating with the controller the operation of the otheractuator to move the at least one printhead by the predetermineddistance and the operation of the inkjets for a predetermined number oftimes.
 18. The method of claim 17 further comprising: receiving from anuser interface with the controller data that identifies the objectwithin the holder.
 19. The method of claim 18 further comprising:operating with the controller the at least one printhead to eject inkdrops with no more than two ink drop volumes.
 20. The method of claim 19further comprising: operating with the controller an ultraviolet (UV)lamp emit light in an UV range to cure UV curable marking materialejected onto the surface of the object from the at least one printhead.